1. Field of the Invention:
This invention relates to a powder disperser for dispersing a powder before the powder is supplied to a classifier.
2. Description of the Prior Art:
It has been known that the factors determinant of the classifying performance of an air classifier generally include the degree of dispersion of the powder within an air flow carrying the powder to the classifier. If the degree of dispersion of powder particles within an air flow is low and the powder comes into classifying chambers in a partially coagulative state, the coagulative particles are classified as coarse particles and are naturally included in a coarse powder. In cases where a fine powder is to be regarded as a classified product, the yield of the operation decreases. If, conversely, the coarse powder is to be regarded as the product, the product has a fine powder mixed therein.
In view of these facts, a classifier is generally provided with a powder dispersing mechanism which is disposed at a stage before the classifying chambers thereof.
However, where the material to be classified is a sticky or coagulant powder, the capacity of the dispersing mechanism within the classifier is sometimes insufficient. For example, in case that the powder includes ultra-fine powder measuring less than 1 .mu.m in a ratio exceeding 50% by weight, the adhesiveness and coagulation of powder suddenly increase to lower the yield and tend to choke up a supply port, etc. of the classifier. To avoid such trouble, it is conceivable to separately provide a disperser at a stage before the classifier for dispersing the powder to increase the degree of dispersion of the powder before it is supplied to the classifier.
FIG. 1 of the accompanying drawings schematically shows by way of example the whole flow of the operation of an air classifying system in which a disperser is arranged in a manner as mentioned above. Referring to FIG. 1, a powder to be processed is supplied from a feeder 1 to a classifier 3 via a disperser 2. A coarse powder portion 5 of the powder is recovered via a rotary valve 4. A fine powder portion 7 is recovered via a bag filter 6. A blower 8 is arranged to keep the air passing through the classifier 3 by suction.
The disperser 2 shown in FIG. 1 functions as a pretreatment device for the classifier 3. However, mere use of the conventionally known mechanical type disperser does not sufficiently meet the requirement for an improved degree of dispersion. The first reason for this insufficiency is as follows: In the case of a disperser 2 using stirring blades, the length of a passage between the disperser 2 and the classifier 3 inevitably increases to a certain extent. Then, recoagulation takes place in the passage to lower the degree of dispersion attained. The second reason resides in that, in order to attain a sufficient degree of dispersion, the powder to be processed must be in a thin state within an air flow. Besides, if it is not thin, sticking of powder to the wall surface of the disperser 2 would impede a continuous operation of the disperser 2 and eventually that of the classifier 3. It is another disadvantage of the mechanical type that the size of the device becomes large.
In view of these disadvantages of the conventional disperser 2, the present inventor has continuously conducted research for a disperser 2 suited for an air classifier 3. The inventor thus has developed a simple disperser 2 of a direct coupling structure. The disperser 2 utilizes an ejector effect obtainable from a high speed air flow. The disperser 2 is capable of efficiently dispersing a powder and supplying a stream of the dispersed powder directly to the supply port of a classifier 3 without any intermediate passage.